The invention relates to magneto-optical disc having an improved surface coating. More particularly, the invention relates to a magneto-optical disc with a protective overcoat that improves the tribological properties and reduces wear.
A variety of media can be used for electronic data storage. In particular, magnetic discs have been used extensively for high density data storage. In addition, optical data storage disc systems are useful for storing large quantities of data. The data is accessed by focusing a light beam, generally a laser beam, onto a data surface of a disc and detecting light reflected from or transmitted through the data surface.
Generally, in optical data storage systems, data is in the form of physical or magnetic marks carried on the surface of the disc. The physical or magnetic marks are detected using the laser light. Phase change and magneto-optical systems provide erasable optical disc systems, which are clearly desirable for certain applications. Magneto-optical systems read data by measuring the rotation of the incident light polarization due to reflection from a magnetic material within the storage medium.
A magneto-optical disc includes a recording layer of a magnetic material. The magnetic material in the recording layer can be magnetized in an oriented direction. The data generally is stored in concentric tracks.
To read data from the disc, an optical pickup device is used. The optical pickup device irradiates the disc with a low power light beam, generally from a laser, and detects the reflected light. Changes in the polarization of the light due to the Kerr effect can be measured in the reflected light. Using the change in polarization, the magnetization of the point on the recording layer can be measured.
To record/write or erase information, the recording layer is heated to a temperature above the Curie temperature by irradiating the material with a more intense light beam, generally from a laser. The magnetization of the heated point on the recording layer can be changed with an external magnetic field. To write data on the disc, a magnetic head is used for supplying the external magnetic field. The same magnet or a separate magnet can be used to erase or initialize the disc.
When only a single magnetic layer is used, it is required to initialize the magnetic layer by aligning the magnetization of the magnetic layer in one direction before writing data. This process can be simplified by using multiple magnetic layers. Two, three or more magnetic layers can be used to facilitate the reading and writing operations. With any of the magneto-optical disc structures, an important design consideration is that light must be able to focus on a magnetic data storage layer having an appropriately selected Curie temperature.
In a first aspect, the invention pertains to a magneto-optical storage medium comprising:
a data storage means for the optical encoding of data; and
protection means for improving the durability of the magneto-optical storage media.
In another aspect, the invention pertains to a magneto-optical storage medium comprising:
a non-magnetic substrate;
a magnetic layer over the non-magnetic substrate, the magnetic layer comprising a magnetic metal or alloy having a Curie temperature accessible by optical heating;
a carbon layer over the magnetic layer.
In a further aspect, the invention pertains to a method of producing a magneto-optical disc comprising depositing a carbon layer onto a disc with a magnetic layer comprising a magnetic metal or alloy having a Curie temperature accessible by optical heating.